1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of esters of fatty acids. More specifically the invention relates to a process for separating an ester of fatty acid from an ester of a rosin acid which process employs an adsorbent comprising silicalite.
2. Description of the Prior Art
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon types from mixtures thereof. As a few examples, a separation process disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491 uses a type A zeolite to separate normal paraffins from branched chain paraffins, and processes described in U.S. Pat. Nos. 3,265,750 and 3,510,423 use type X or type Y zeolites to separate olefinic hydrocarbons from paraffinic hydrocarbons. In addition to their use in processes for separating hydrocarbon types, X and Y zeolites have been employed in processes to separate individual hydrocarbon isomers. As a few examples, adsorbents comprising X and Y zeolites are used in the process described in the U.S. Pat. No. 3,114,782 to separate alkyl-trisubstituted benzene isomers; in the process described in U.S. Pat. No. 3,864,416 to separate alkyl-tetrasubstituted monocyclic aromatic isomers; and in the process described in U.S. Pat. No. 3,668,267 to separate specific alkyl-substituted naphthalenes. Because of the commercial importance of para-xylene, perhaps the more well-known and extensively used hydrocarbon isomer separation processes are those for separating para-xylene from a mixture of C.sub.8 aromatics. In processes described in U.S. Pat. Nos. 3,558,730; 3,558,732; 3,626,020; 3,663,638; and 3,734,974, for example, adsorbents comprising particular zeolites are used to separate para-xylene from feed mixtures comprising para-xylene and at least one other xylene isomer by selectively adsorbing para-xylene over the other xylene isomers.
In contrast, this invention relates to the separation of non-hydrocarbons and more specifically to the separation of fatty acid esters. It has been discovered that an adsorbent comprising silicalite exhibits adsorptive selectivity for an ester of a fatty acid with respect to an ester of a rosin acid thereby making separation of such esters by solid-bed selective adsorption possible. In a specific embodiment this process is a process for separating the esters of the fatty acids from the esters of the rosin acids in tall oil.
Production of fatty esters is the most important phase in the industrial chemistry of fatty acids. The esters produced are of several types and include those resulting from the reaction of fatty acids with monohydric alcohols, polyhydric alcohols, ethylene or propylene oxide, and acetylene or vinyl acetate. The principal monohydric alcohols are methanol, 1-propanol, 2-propanol and 1 -butanol. The greatest uses of esters are in the solvent and plasticizer fields. Esters of monohydric alcohols are used for plasticizers and in cosmetics. Esters of saturated fatty acids are of value in compounding lubricating oil, as a lubricant for the textile and molding trade, in special lacquers, as a waterproofing agent, and in the cosmetic and pharmaceutical fields. Esters of unsaturated fatty acids find use as drying agents.
It is known from U.S. Pat. No. 4,048,205 to use type X and type Y zeolites for the separation of unsaturated from saturated esters of fatty acids. The type X and type Y zeolites, however, will not separate the esters of rosin acids found in tall oil from the esters of fatty acids, apparently because the pore sizes of these zeolites (over 7 angstroms) are large enough to accommodate and retain the relatively large diameter molecules of esters of rosin acids as well as the smaller diameter molecules of esters of fatty acids. Type A zeolite, on the other hand, has a pore size (about 5 angstroms) which is unable to accommodate either of the above type esters and is, therefore, unable to separate them.
We have discovered that silicalite, a non-zeolitic hydrophobic crystalline silica molecular sieve, is uniquely suitable for the separation process of this invention.